I don’t know about you, but I’ve always been a little afraid to run queries directly on my WordPress database. This post goes through how to accomplish many tasks using queries. Sometimes the task of going post by post to make a change would take you 10 times as long as just running a simple query.
(I use the WP-DBManager plugin to manage database backups and optimization, and it has a panel where you can run queries on your database, so you wouldn’t even need to figure out how to get into PHP MyAdmin to run these queries.)